Pipe Flow Rate from Pressure Calculator
Calculate the volumetric flow rate based on pressure and pipe diameter.
How to Calculate Flow Rate from Pressure
Calculating the flow rate of a fluid through a pipe based on pressure requires an understanding of fluid dynamics, specifically Bernoulli's Principle. When liquid is forced through an opening or a pipe at a specific pressure, that potential energy is converted into kinetic energy (velocity).
The standard formula used for calculating flow from a discharge point (like a nozzle or the end of a pipe) is:
Q = 29.84 × C × d² × √P
- Q: Flow rate in Gallons Per Minute (GPM).
- C: Discharge coefficient (accounts for friction and turbulence).
- d: Internal diameter of the pipe in inches.
- P: Pressure at the discharge point in PSI.
Key Factors Influencing Flow
1. Pipe Diameter: Flow rate increases with the square of the diameter. Doubling the pipe size doesn't just double the flow; it quadruples the potential volume capacity.
2. Pressure: The relationship between pressure and flow is non-linear. Flow is proportional to the square root of the pressure. To double your flow rate, you would need to increase the pressure by four times.
3. Discharge Coefficient (C): This represents the efficiency of the flow. A perfectly smooth, well-machined nozzle might have a C of 0.99, while a sharp-edged orifice might be as low as 0.60 to 0.65.
Example Calculation
Suppose you have a 2-inch pipe with a measured pressure of 40 PSI and a discharge coefficient of 0.98:
- Square the diameter: 2 × 2 = 4
- Find the square root of pressure: √40 ≈ 6.32
- Multiply: 29.84 × 0.98 × 4 × 6.32 = 739.26 GPM
Important Considerations
This calculation assumes "free discharge" into the atmosphere. If you are calculating the flow between two points in a closed system, you must use the Pressure Drop (ΔP)—the difference between the upstream and downstream pressure—rather than just the static pressure.